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This paper describes the development and use of a direct tension test for measuring the strength and failure strain of asphalt binders. This test, which is used to determine the strain at failure (strain tolerance) of asphalt binders, was selected by the Strategic Highway Research Program (SHRP) as a specification test for asphalt binders. Test methods available prior to the development of this test were found inadequate for accurately measuring the strain tolerance of asphalt binders. Therefore, these methods were judged unsuitable for specification purposes. The dog bone geometry used in the direct tension test method described in this paper is widely used for other materials. Each specimen requires slightly more than three grams of asphalt binder. The specimen is gripped using plastic inserts cast as an integral part of the test specimen. The specimen is loaded through holes in the inserts using specially designed pins that automatically align the test specimen. Specimen elongation is measured using a noncontact laser-based extensometer which provides accurate and repeatable measurements. The method is easy to use and is designed to provide the strain-at-failure-data needed for specification purposes.
direct tension, asphalt cement, asphalt binders, fracture, stress-strain curve, failure
Professor of Civil Engineering, The Pennsylvania State University, University Park, PA
Research Assistant, The Pennsylvania State University, University Park, PA